What causes an echo? An echo is a reflection of sound, ‘bouncing’ off a surface and arriving at the listener shortly afterwards. But several other things need to happen in order to hear an echo; after all, you very rarely hear your own voice reverberating back when you shout in your own home…
Our ears cannot distinguish an echo if the delay from the original sound is less than a tenthof a second. So one requirement is distance from the surface the sound reflects off.
Additionally, in order for the sound to return to its source (i.e. you!), a sufficient amount of the original sound needs to hit a large enough surface. If you don’t shout very loud or if the surface that the noise is directed at is too small, very little sound will hit and bounce back. Any sound that does hit the surface will reflect at the same angle at which it hit, so – as well as the size – a smooth surface will also help return an echo. And having several smooth surfaces will help return more of the original sound to your ears.
But something else usually needs to happen in order to hear an echo – other sounds need to be drowned out. It’s difficult to hear echoes in a busy town for example due to all of the other noise from cars, people, birds, sirens, etc.
So there we have it. An echo is the reflection of sound under certain conditions including distance, the original volume of the sound, large and flat enough surfaces to reflect from and a lack of other noise.
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